Although the census is recorded at individual household level, data is aggregated for publication in order to protect the privacy of census respondants. The primary unit of published data is the Output Area at the most local level and local authorities (districts, counties, boroughs etc) at higher levels.
Output Areas are the basic building block of published census data. Each normally contains between 40 and 250 households with a normal resident population of between 100 and 625 people. The aim is to ensure that all Output Areas have a comparable resident population, so their geographic size will differ considerably between urban and rural areas.
Where possible, Output Areas are either wholly urban or wholly rural and don't cross administrative borders such as local authority wards. However, small rural villages and hamlets may not be large enough to fit this structure, so rural settlements may be disjoint from their associated Output Areas.
Some Output Areas may contain more than 625 people if they contain a single institution with a very large number of residents, for example a prison.
Output Areas are grouped into Lower layer Super Output Areas (LSOAs) and Middle layer Super Output Areas (MSOAs). There are typically four or five Output Areas in an LSOA, and four or five LSOAs in an MSOA. These provide census statistics at a less fine-grained level.
Local Authorities and Local Authority Wards
At higher level, census data is published for every principal local authority in England and Wales - that is, districts, boroughs, counties and unitary authorities - and their electoral wards as of 2022.
Some census data with particularly small values for minority responses (for example, gender identity) is only published at local authority level and above. Detailed figures for age by individual year is also only published at local authority level and above. This is because, with a very small number of respondants selecting a particular option within an Output Area, it would potentially be possible to identify individuals or households from the published data.
Other Published Geographies
As of February 2023, the ONS has also published census data for Regions and Countries. These datasets have been incorporated into this website.
As well as the geographies for which data is published by the ONS, we have also carried out a "best fit" calculation of data for Combined Authorities, Metropolitan Counties, Civil Parishes/Communities and Built-Up Areas. These are calculated by aggregating the data from the Output Areas or Local Authorities within them. Care should be taken when using these figures as, particularly at the more local levels, they may not precisely coincide with discrete Output Areas.
The ONS has stated plans to release datasets for more geographies, including some of those that we have calculated in the interim. If/when the official data is published for any of our calculated geographies, we will replace that with the official data and update the site accordingly.